Note: Descriptions are shown in the official language in which they were submitted.
~o 7 39 82 5D-5364
The present invention relates to electrical
separable connector modules for connecting together the
operating components of an underground power distribution
system by means of shielded electrical cable.
Separable connector assemblies for underground
power distribution cable, or shielded cable, are watertight
then assembled and may be readily separated into two or
more units to break a cable connection. As such units are
available separately commercially for various reasons and
are individually subject to special design considerations,
they are commonly referred to as "modules". Thus, a
connection includes two or more matching modules assembled
together.
One type of separable connector commonly used is
known as a "rod and bore" type. A bore connector module
having a receiving bore in a shielded, insulating housing
and a grasping contact member in the bore receives a
matching rod connector module having rod contact extending
axially along a receiying passageway, or cone, in the rod
housing for receiving the matching portion of the bore
module. The rod is inserted in the bore and grasped by the
bore contact member. Examples of this type of connector
are described, for example, in the following U.S. Patents :
3,513,437 issued 19 May 1970 to W.A. Morris
~3,542,986 issued 24 Nov. 1970 to E.J. Kotski
3,551,587 issued 29 Dec. 1970 to R.F. Propst
3,587,035 issued 22 June 1971 to E.J. Kotski, and
-3,955,874 issued 11 May 1976 to V.J. Boliver
A rod module generally has an elastomeric
insulating housing with an outer conductive shield layer
connected to ground. me housing has a cable entrance
opening at one end through which a cable is electrically
10~398Z 5D-5364
connected to an embedded crimp connector fixture. The
fixture is surrounded by a conductive shielding insert layer
of elastomer for assuring that there are no voids between
the conductive internal components and the insulating
housing material. The housing is additionally provided at
another end with an elongated passageway extending from an
open exterior end toward the fixture. A conductive contact
rod is fixed at one end to the crimp fixture and extends
along the axis of the passageway. The configuration of the
passageway is that of a truncated circular cone segment
tapering in toward the insert and therefore the passageway
is commonly referred to as the "cone". The cone is adapted
to receive a bore module housing portion of matched
configuration with a receiving bore for guiding the contact
rod to a set of female contacts. The exterior end of the
well may additionally be provided with a short skirt of
elastomer to prevent restrike to the ground shield through
ionized gases generated by arcing in the bore when energized
modules are disconnected.
It has been found that when such rod modules as
described above are used for disconnecting energized cable
of relatively high distribution voltages, such as, for
example, 12 kilovolts and higher, an audible corona can
arise inside the cone of the rod module after disconnection.
m is corona will in some cases result in a dielectric
breakdown of the arc-generated gases in the cone and cause
the rod contact to be short circuited to the grounded
shield of the housing or other adjacent grounded surfaces.
The novel rod module is provided with a resistive
stress relief layer on the inside surface of the cone and
electrically connected to the rod.
The stress relief layer prevents corona and
107398Z 5D-5364
subsequent dielectric breakdown in the cone without otherwise
interferring with the operation of the module.
The stress relief layer additionally reduces the
likelihood of premature arcing between the rod and matching
female contacts in the making of a connection on three-phase
applications, in which there is a greater voltage between
the rod and female contacts.
FIGURE 1 is a partially-sectioned side view of a
partially-engaged matching pair of separable connector
modules in accordance with the preferred embodiment of the
present invention.
A preferred embodiment of the present invention
is the elbow type rod module 10 shown in FIGURE 1 of the
drawings in partial engagement with a matching bore module 12.
The rod module 10 has an elastomeric housing 14
with a cable entrance 16 at one end for a cable 18 and a
cone 20 in another end. A conductive grounded shield layer 22
extends over most of the outer surface of the housing 14
and is connected by a lead 24 and the cable shielding to
ground. A metal crimp fixture 26, shown in phantom lines is
disposed inside the housing 14 and connected to the
conductor of the cable 18. A conductive shield coating
insert 28, also shown in phantom lines, surrounds the
fixture 26.
Axially disposed in the cone 20 with one end
rigidly attached to the fixture 26 is a metal contact rod 30
with an ablative follower 32. At the outer rim of the cone 20
is a gas shield 34.
The entire inside surface of the cone 20 is
covered with a resistive stress relief layer 36 of carbon
loaded elastomer having a thickness of about 1.25 millimeters
to about 2 millimeters and a volume resistivity of about
107 3982 5D-5364
3 x 108 ohm - centimeters. The layer 36 is electrically
connected at the bottom of the cone 20 to the conductive
shield insert 28 and thus also to the fixture 26.
The resistive layer 36 gradually attenuates the
voltage along its axial length and thereby eliminates highly
concentrated field stress which might generate corona.
The stress relief layer specifications may be
varied within limits.
The layer must extend a certain minimum distance
axially to be effective in reducing the field stress. As
a practical matter, the minimum length should be at least
about 3 centimeters for a connector rated at 8.3 kilovolts
and should be greater for connectors of higher ratings.
The stress relief layer should also have a minimum
total resistance at the operating voltage along its entire
length of about 10 megohms. If the total resistance is too
low, the stress which without the layer was concentrated in
the bottom of the core will simply be moved to the outer
end of the layer 36 to cause similar corona problems there.
If the resistance of the layer is too high, on the
other hand, the stress grading effect of the layer will
again be diminished since most of the voltage attenuation
will be in that portion immediately adjacent the inner end
of the rod. The total resistance of the layer along its
axial length should therefore not be much greater than
about 1000 megohms.
-- 4 --
